Medical diagnosis is utilizing diverse approaches of obtaining images of humans and animals such as X-ray, computer tomography, nuclear-spin-resonance and ultrasonics. The straight forward photography is of lesser importance as it merely records the external appearance of skin portions of humans and animals while the other methods present specific views especially of the inner portions of the body which are more suitable for the diagnosis.
More recently the recording of impedance and other electrical images was developed. The use of single electrodes including the independent handling of several electrodes for the recording of the electrical properties such as the impedance typically as a function of time is well known for many decades, especially in the fields of electro-cardiography (ECG or EKG) and electro-encephalography (EEG). In these cases typically the individual electrodes are attached to the skin by some means such as suction devices or adhesives. Furthermore, these electrodes are provided with a relatively large surface having the order of magnitude of about 1 sq. cm which consists of metals, conductive gels or conductive adhesives. Typically the electrical properties are recorded as a function of time. However, the recent developments utilizes arrays of these electrodes where each of them records the electrical properties such as the impedance or conductivity in a manner that all these values are simultaneously recorded and for example brought onto a display like a monitor. This then provides images yielding information which is significantly different from the images of the other diagnostic methods as stated above. The known specific configurations will be referred to in more detail below.
A particular area of interest is the diagnosis of cancer where it is of interest to investigate the skin primarily related to breast cancer and skin cancer. The article “Overview of Skin Cancer Detection and Prevention for the Primary Care Physician” by A.3. Bruce et al. of the Mayo Clin. Proc. 2000; 75; 491–500 describes the diagnostic possibilities for a primary evaluation of the skin with respect to the detection of specific cancers. This article states that the initial visual inspection by the physician is a meaningful first step in order to decide whether or not further investigations will be necessary. However, it is desirable after the immediate first visual inspection to develop another rather simple method for identifying whether or not cancer can be diagnosed.
WO-A-97/47235 provides a method of a dermal diagnostic analysis through the use of a digital camera which allows a somewhat more sophisticated approach through the recording of the critical portions of the skin.
WO-A-98/09155 shows a step further, it includes to apply a chemical to the critical skin area and after several hours this area is illuminated with ultraviolet light and the fluorescent irradiation can be recorded through picturing spectroscopy. This allows to identify cancerous portions of the skin. This method, however, is time consuming and cumbersome and still requires additional diagnostic methods in most of the cases.
A number of possibilities have become known which utilize the determination of the electrical properties of the skin.
U.S. Pat. No. 5,928,159 describes an apparatus and methods utilizing a probe provided with several electrodes which is applied to a skin portion that might be cancerous and the electrical data of these portions are recorded in comparison with a normal neighbour portion of skin.
U.S. Pat. No. 5,143,079 describes an apparatus for the detection of tumors in tissues. It utilizes a probe with a fixed arrangement of electrodes, e.g. 64 elements arranged in an 8×8 array. These electrodes have a hexagonal form, the electrodes being of gold plated printed copper for example. The hexagons typically have sides of 10 mm. These electrodes by themselves are still rather large so that only a fairly small number of them can be utilized in the probe and, therefore, a real image cannot be generated.
A further development is described in U.S. Pat. No. 5,810,742 and the article “T-SCAN™ as a Diagnostic Tool for Breast Cancer” by M. Assenheimer et al. accessible in the Internet through www.transscan.co.il/publication1.html. The described systems have a fairly large number of individual electrodes allowing to generate an image of having a reasonable resolution. The electrodes described are typically in a rectangular array with a multiplicity of wells which are separated by dividers consisting of insulating material. These wells are filled with a hydro-gel or conductive gel and the wells themselves are provided with a metal electrode which projects to the portion below the electrode so that the entire configuration can be applied onto a printed circuit board (PCB) which has a corresponding array of electrodes. In this manner a discardable article is generated. This is of importance as for well known reasons it is not advisable to use electrode configurations for more than a single patient. The PCB as such has an array of conductive paths which are guided to a multi-pin connector which then is connected through a cable to the evaluation computer which is capable of recording the electrical characteristics of each individual electrode so that the desired image can be generated in the computer and displayed on the monitor. The use of wells filled with a conductive gel has the disadvantage of being difficult to manufacture thus being expensive which is critical for such a discardable article. Furthermore, the spacing between these wells is limited which reduces the resolution of the desired image. This is of particular importance as critical skin portions which might be cancerous only have dimensions of a few millimeters and, therefore, for obtaining a good resolution pitches of the wells in the order of several tenths of a millimeter are required.
The use of multiple electrodes or arrays of electrodes is well known and described in a large number of publications.
U.S. Pat. No. 3,490,439 describes an assembly of electrodes used for electro-encephalography. The electrodes as such are small foam balls coated with a conductive cloth piece.
U.S. Pat. No. 5,452,718 presents an electrode configuration in which a conductive material having a tip is embedded in a plastic ferrule.
U.S. Pat. No. 3,896,790 relates to a brain wave sensor in which a single electrode is used which consists of several prongs which ensure a good electrical contact, even in the presence of hair.
In the above cited references all these electrodes essentially are still separate from each other. Configurations are also known in which a multiplicity of electrodes is arranged in a fixed mutual configuration. This is described for example in U.S. Pat. No. 5,184,620, U.S. Pat. No. 4,353,372 and U.S. Pat. No. 6,055,448. In all these cases the electrodes are embedded into a common carrier, however, they are still used for the typical ECG or EEG application which means that despite their fixed spacial relationship they are individually used and usually only their time dependence is recorded.
In all electrodes and electrode arrays described above configurations are shown in which the electrodes themselves have a relatively large surface and they are typically directly applied to the outer surface of the skin. There are alternative methods of utilizing electrodes which essentially consist of individual needles. These needles operate in a somewhat different manner. If properly applied they allow to penetrate the outermost portion of the skin and provide a more valuable determination of the electrical properties which for the recording of the image appears to be advantageous.
A needle electrode is described in U.S. Pat. No. 5,482,038 where an individual sharp needle is inserted into a special holding device which allows to establish a defined pressure. Needles of this type are used for example in neurological examinations using an electro-myograph (EMG).
Similar configurations can be taken from the references U.S. Pat. No. 5,509,822 and EP-A-0 533 487 which are either used for electro-myography or for electro-cardiography. These needles are either a multiplicity of several components that are handled independently but connected to a common monitoring system or configurations in which a pair of needles is used.
EP-A-0 538 739 describes an array of needles, the number ranging between 50 and 150. These needles are brought into a common plastic holder. The needles themselves have a solid configuration with a relatively sharp pin similar to those used in acupuncture. Each needle is provided with a spring allowing to apply all needles with a given pressure. The array is a pre-determined geometrical configuration typically having an overall circular circumference. The data, however, are collected individually from each electrode and utilized in some kind of a statistical evaluation. There is no intention to record an image. Furthermore, the reference is silent with respect to the establishment of the electrical contacts between these needles and the cable leading to the electronic evaluation unit.
DE-U-92 18 879 relates to an array of electrodes for the determination of the distribution of electrical potentials on the skin of a patient. It shows multiplicities of electrodes for the above described purpose and the object of this reference is to replace this multiplicity of electrodes by a foil having semi-conductive layers which is scanned for example by a laser beam causing a temporary conductivity of a small portion of the foil thus replacing a multiplicity of electrodes by such a foil which is scanned through point by point. No reference is made at all to the type of electrode configurations used.
DE-U-85 02 291 describes arrays of needle electrodes for biomedical applications where each electrode is individually connected to a cable so that a multiplicity of signals can be recorded. No reference is made to the possibility of recording an electrical image.
WO-A-87/07825 describes an electrode and the related method of manufacture. A base carrier contains an arrangement of conducting protuberances arising from the base serving as the electrodes. These electrodes are individually connected to an electrical path that is leading to an array of contact areas which allow to transfer the signal to a recording unit. The protuberances or needles have the shape of cones. These cones are grown on a multi-layer configuration and typically have dimensions up to 25 microns. This means that they are relatively small and their primary use is in the area of neurology. The needles allow to penetrate the surface of the tissue to be diagnosed.
U.S. Pat. No. 5,215,088 describes a three-dimensional multi-electrode device especially useful as a neuron interface. The electrodes are electrically isolated from each other, the signals are typically transmitted using a multiplexing circuitry. The needles typically consist of semi-conductive material on the basis of silicon. In a block of such material sequences of cuts are obtained using a saw utilized in the microelectronic industry. This is performed in two directions so that an array of pins is obtained having a rectangular or square cross-section. In a subsequent etching process material is taken away from the upper portions of these columns so that they obtain a needle-like form. This is particularly suitable for neuron-type applications e.g. a prosthesis for a blind person. The process is rather complicated and thus expensive, needle arrays of this configuration do not appear to be suitable as single use throw-away articles because of the high cost.
Arrays of needles as electrodes require to bring them into a defined array by simultaneously electrically isolating them from each other. For instance this could be performed by bringing a multiplicity of contact pins into a plastic body, for example through an injection molding or casting method. The use of these techniques, however, is cumbersome and not very cost effective which is critical for an article that preferably should be discardable. The problem becomes even more critical when moving in the direction of smaller pitches, for example well below 1 mm. The handling of individual needles or pins will be increasingly difficult thus resulting in unacceptably high manufacturing cost.
Arrays of needles or needle-like configurations are of primary interest for the medical diagnosis and therapy of the skin or other organs and tissues of humans and animals. Such an array of electrodes, however, might also be useful for other configurations whenever it is possible to establish electrical contact with the component to be investigated and when the determination of an impedance or electrical image provides meaningful information. This typically applies to components which do not have a hard outer surface because in this case only individual electrodes would establish an electrical contact. Therefore, components of interest are typically softer on their surface like elastomeric and similar components.